PARENT SESSION
Thursday, August 10, 8:00-11:30 am
COS 78 - Nitrogen cycling I
L-4, Lobby Level, Cook Convention Center
Presiders: K Buckeridge
Variations in nitrification potential in manured agroecosystems of contrasting soil type.
Fortuna, Ann-Marie *,1, Honeycutt, C. Wayne 1, Marsh, Terence2, 1 USDA-ARS, NEPSWL, University of Maine, Orono, ME2 Center for Microbial Ecology, Dept. of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI
ABSTRACT- The rates of immobilization and conversion of NH4 to NO3 and NH3 in dairy slurry vary with abiotic and biotic factors affected by soil type. Current manure management guidelines are often based on net N fluxes in loams. Best management practices should reflect variations in soil type, plant community, nutrient status and disturbance. Samples were collected at USDA-ARS research sites across a variety of ecoregions and soil types in grassland and agronomic systems. Each soil series was used in a 30 d incubation containing 5 time intervals (0, 7, 14, 21 and 28d), two managements (dairy slurry 300 kg N ha-1 amended soil and a soil control) and 4 replicates. Subsamples were removed at each interval for analyses of 2 M KCl extractable N and measurement of nitrification potential determined via the shaken slurry method. Nitrification rates on controls for a given soil did not vary. Soils containing 20 to 30% clay and 15 to 20 % sand had the highest control rates (10 to 11 mg N kg-1 soil d-1). Nitrification potentials in manure amended soils ranged from 2.6 (day 0) to 20 mg N kg-1 soil d-1. Manuring doubled or tripled nitrification potentials on all soils except the vertisol. Soils with a history of high N inputs had greater potential nitrification rates. Soils with low N inputs showed the greatest increase in nitrification rate with manure addition. Determining variations in the timing and release of N from manure can reduce loss of manure N and improve best management practices.
Key words: nitrification potential, manure, soil type